Magnetite anodes for use in impressed current cathodic corrosion protection are known in the art and have proved superior to traditional silicon-iron and graphite anodes which require frequent replacement. Thus, a magnetite anode, the entire inside surface of which is plated with a thin copper layer, and in which just below the anode top a copper plate is fixed to the inside copper layer with a cable connection attachment soldered thereon, has been described and used in practice for cathodic protection of a number of structures susceptible to corrosion. In this context, reference is made to my paper entitled "Magnetite Anodes For Impressed Current Cathodic Protection", presented during "Corrosion/78" (paper 159), March 1978, Houston Tex., and published in "Materials Performance", August 1979, pp. 17-20. The latter reference is believed to contain a description of the prior art coming closest to the present invention as described and claimed herein.
The above-mentioned prior art anodes have a number of disadvantages. Thus, the cable connection attachment at the top of the anode has given rise to problems with respect to the current distribution and hence also as regards the so-called end-effects, i.e. a high load and thus also metal plating attacks at those locations on the anode where an uneven current load is encountered.
Furthermore, when using a copper plating or coating combined with the prior art cable connection attachment, problems with respect to cracks in the magnetite anode were experienced. Thus, when cracks were formed, the electrolyte could penetrate the cracks, and the copper layer disappeared at the crack locations. This caused problems with regard to the current discharge, since at those locations on the anode where the copper layer disappeared, the current could not pass, and hence the remaining part of the anode was unduly highly loaded. Furthermore, an unduly high resistivity was experienced because of the disappearance of the copper layer.
In accordance with the above, it is an object of the present invention to provide an improved oxide anode arrangement for use in impressed current cathodic corrosion protection, thereby providing an anode having a satisfactory even distribution of current therefrom and not being susceptible to end-effects, at the same time avoiding an unduly high anode resistivity.
It is a further object of the invention to provide an improved magnetite anode of the above type which has the above advantages and is simple and cheap in production and practical use.
A still further object of the invention is to provide a magnetite anode of the above type having a coating or plating consisting of lead metal or a lead metal alloy, such anode being particularly effective in operation in impressed current cathodic protection.
Still further objects will be apparent from the following description.